Tetrahedral oxidations with halogens

Arsenic, Antimony and Bismuth. These elements are obtained by reduction of their oxides with hydrogen or carbon. For As and Sb unstable yellow allotropes, presumably containing tetrahedral As4 and Sb4 molecules, can be obtained by rapid condensation of vapors. They are easily transformed into the stable forms, and yellow Sb is stable only at very low temperatures. Bismuth does not occur in a yellow form. The normal forms of As, Sb and Bi are bright and metallic in appearance and have crystal structures similar to that of black P. When heated, the metals burn in air to form the oxides, and they react directly and readily with halogens and some other non-metals. They form alloys with various other metals. Dilute non-oxidizing acids are without effect on them. With nitric acid, As gives arsenic acid, Sb gives the trioxide and Bi dissolves to form the nitrate. 

Boron has a great affinity for oxygen and occurs in nature only in boric acid or borates. Borates are composed from clusters of flat trigonal BO3 and tetrahedral BO4 groups. The structural chemistry of borates is as rich and complicated as those of silicates, borides, or boranes. Boron oxide is an essential part of borosilicate glasses such as Pyrex. Boron halides are volatile molecular compounds. They are Lewis acids and react violently with water. The subhalides consist of boron chains or clusters that have terminally bound halogen atoms. They are substitution derivatives of the lower boranes. 

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